The present invention relates to surface or form grinding machines, especially to improvements in machines for grinding of complex metallic workpieces. Typical examples of workpieces which can be treated in machines of the present invention are turbine blades. More particularly, the invention relates to improvements in grinding machines of the type wherein one or more grinding spindles serve to rotate grinding wheels and, in the case of a machine with two spindles, the spindles are parallel to each other and are movable radially toward and away from each other. Still more particularly, the invention relates to improvements in grinding machines of the type wherein the workpiece is mounted in a holder which is movable axially as well as tangentially of each grinding wheel. As a rule, such grinding machines are further provided with means for dressing or restoring the working surface or surfaces of the grinding wheel or wheels.
Precision form grinding of complex workpieces which have a plurality of uneven surfaces in presently known grinding machines is a complicated and costly procedure which involves the use of sophisticated control equipment and resort to specially designed modern grinding machines. Surface grinding of blanks of turbine blades is a typcial example of a complex grinding operation because such blanks exhibit a large number of uneven (concave, convex, twisted and analogous hard-to-treat) external surfaces. Therefore, the treatment of a complete turbine blade often involves an extraordinarily large number of successive grinding operations each of which includes the removal of material from a relatively small portion of the workpiece. In accordance with presently known techniques, turbine blades and workpieces of equally complex design are treated in a production line which employs a series of discrete grinding machines each of which is designed to remove material from a specific portion of the workpiece. The workpiece is transported from grinding machine to grinding machine, and each such machine has a specially designed grinding tool for the treatment of the corresponding specific portion of the workpiece. It is possible to provide such production lines with automatic or semiautomatic conveyor systems which transport the workpieces between successive grinding machines; however, this involves additional expenditures and contributes to the space requirements of the production line as well as to complexity, sensitivity and cost of automatic controls for the production line. Furthermore, the dimensions of the ultimate products are likely to deviate from the desired optimum dimensions for a variety of reasons such as the need to repeatedly release and clamp a workpiece preparatory and subsequent to transfer into the next-following grinding machine of the production line, the likelihood of inaccurate positioning of a workpiece in a given grinding machine with attendant removal of insufficient or excessive quantities of material from the corresponding portions of the workpiece, accidental damage to finished portions of a workpiece and/or unequal wear upon the component parts of discrete grinding machines and/or upon the means for transporting workpieces between such machine. In addition, the operation is time-consuming because each releasing, transporting and clamping step adds to the interval which is needed to complete the treatment of a workpiece. Additional time is lost because the output of the production line is dependent upon the operation of the slowest link, e.g., upon the operation of that grinding machine which requires the longest interval of time to complete the treatment of the corresponding specific portion of a workpiece. Still another drawback of such production lines is that each conversion for treatment of differently dimensioned and/or configurated workpieces is very time consuming so that the production lines are not sufficiently economical for the treatment of short or medium-long series of identical workpieces. A further drawback of a production line with an entire battery of serially arranged grinding machines is that all or nearly all of its machines are utilized well below capacity (due to the aforementioned fact that the interval of dwell of workpieces in each of several machines is determined by the interval of dwell in the slowest machine, i.e., in that machine which requires a relatively long period of time to complete the treatment of the corresponding portion of the workpiece). Last but not least, the entire production line must be arrested in response to malfunctioning of a single component, e.g., in response to temporary idling of a single machine of a full battery of discrete grinding machines. Therefore, such production lines are rather uneconomical except under certain exceptional circumstances, e.g., the need to grind a long series of identical complex workpieces. Even if the lack of economy is acceptable to certain manufacturers, the likelihood of deviation of dimensions of the ultimate product from optimum dimensions (primarily due to the need for repeated clamping and releasing of one and the same workpiece and the resulting danger of inaccurate positioning with reference to the grinding wheel in a machine) has deterred many potential purchasers from investing into such production lines.
It is already known to provide a grinding machine with two parallel spindles each of which carries a grinding wheel so that a workpiece can be treated, at the same time, by two discrete material removing tools. A machine which embodies pairs of spindles for discrete grinding wheels is known as Blohm 310/DK and is manufactured by the assignee of the present application. Such conventional machine is used for grinding of turbine blades and similar complex workpieces. However, even though two portions of one and the same workpiece can be treated in a simultaneous operation, complete grinding of an entire turbine blade still necessitates resort to several grinding machines and to appurtenant auxiliary equipment including conveyors and like apparatus. For example, the treatment of five differently configurated portions of a turbine blade necessitates the utilization of at least three discrete grinding machines with pairs of spindle for grinding wheels.
German Offenlegungsschrift No. 21 22 763 discloses a grinding machine which is specifically designed for the treatment of turbine blades. The treatment resembles that of workpieces in copying lathes, i.e., the configuration of a pattern is tracked and the position of the grinding wheel is changed accordingly. It has been found that the machine of the just mentioned German printed publication is not capable of treating complex portions of turbine blades or like workpieces with a desired degree of precision. At the very best, the machine is useful for grinding of those portions of workpieces which exhibit relatively large and simple surfaces. Typical examples of such relatively simple portions are the leaves of turbine blades; however, the more complex portions of such workpieces (e.g., those known as fir tree roots) must be treated in different types of grinding machines in accordance with the aforedescribed conventional technique involving the use of a discrete grinding machine for the grinding of each specific portion of the corresponding part of a turbine blade, namely, each portion whose surface is concave, convex, twisted or constitutes a combination of such surfaces.